CHAPTER 1 INTRODUCTION
2.8 Specific InterventiOn
To promote the importance of social capital/cohesion in urban health development and planning there is a need to measure and monitor these variables and the health impacts. Therc ers and thc health sector here. in documenting health outcoulics is a key role for health work
and disseminating findings to increase recognition of the value of social sector intervcntiOIi.
There is also room for other sectors such as water and sanitation, transport and education to recognize the role they have to play in social and health development for better health eqtuit.
2. 9 Biological Effects of Radiation
The interaction of ionizing radiation with the human body, arising either from external sources outside the body or from internal contamination of the body by radioactive substances, leads to biological effects which may later come as clinical symptoms (Martin, 1979). The nature and severity of these symptoms and the time at which they appear depend on the amount of
radiation absorbed and the rate at which it is received.
While ionizing radiation has many uses, some of great benefit to mankind, it is also tnie that refully weighed against possible delirious effects. ionizing its beneficial use must be ca
radiation is not only potentially dangerous, but in fact lethal, if misused. The effects which occur depend on the types of cells which absorb the radiation, the total radiation dose. the length of time over which the exposure occurred, and whether the body is able to affect any repair of the damage. Differences in biological effects are the result of differences in these factors. The biological effects of radiation may be broadly classified into two categories, viz.
non-stochastic (deterministic) and stochastic effect (Cembcr, 1989).
Non_stochastic Effects
Effects with a threshold dose and for which the severity of the injury increases with dose arc known as non-stochastic effects. Non-stochastic effects are characterized by three quantities:
First, a certain minimum dose must be exceeded before the particular effect is observed.
Additionally, the magnitude of the effect increases with the increase of the dose. Furthermore, there is a clear causal relationship between dose agent and effect in a given individual, in a word. in non-stochastic effect, a certain minimum dose must be exceeded before the particular effect is observed, and the magnitude of the effect increases with the increase of the dose. For example, a person must exceed a certain amount of alcohol before he shows signs of drinking.
After that, the effect of the alcohol depends on how much he drank.BecaUSe of the minimum dose that must be exceeded before an individual shows the effect, non-stochastic effects are also called threshold effects. on-stochastic effects are also can be termed as early radiation effects. Examples: Erytherna, cataract, radiation damage to the gut and the production of th
N
e temporary or permanent sterility in both males and females. When the magnitude of the effect or the proportion (percent) of individuals who respond at a given dose is plotted as a function
1) U
of dose to obtain a quantitative relationship, the doscre5POflSe cue A of Figure 2.9 s obtained, in Figure 2.9. A point 'a' represents the threshold point.
Stochastic Effects
Stochastic effects are those effects that occur by chance. They occur among unexposed people as well as among exposed individuals. Stochastic effects are therefore not clearly related to exposure. The main stochastic effects are cancer and genetic effects. The result of exposure to a carcinogen (substance that produces cancer, tobacco) increases the probability of occurrence of the effect. In this case, the increase in probability of the effect is directly propoiOflal to the dose.
)O
r
'p ci.
D o s e
Dose-response curves for non-stochastic (A) and stochastic (B) effects.
People may develop cancer whether they are exposed to carcinogenic agents or not. However, exposure to carcinogen increases he likelihood of cancer. Lung cancer is found in a much
higher proportion of cigarette smoKers than among non-smoker, and among cigarette smokers, lung cancer is seen in a greater proportion of heavy smokers than in light smokers.
In other word, as the name implies, stochastic effects occur in a statistical manner. For radiation induced effects, the probability of a stochastic effect occurring depends upon the radiation dose received, but there is no such thing as a "safe dose" i.e., no threshold dose exists below which such an effect can't occur. Two general types of stochastic effect are well recognized. The first occurs in somatic cells and may result in the induction of cancer in the exposed person; the second occurs in cells of the germinal tissue and may result in hereditary disorders in the progeny of those irradiated (Islam, 2009).
Another important point concerning such stochastic effects as mentioned earlier, is that the severity of the effect is unrelated to radiation dose. Thus, as the radiation dose increases, the probability of cancer induction increases, but the severity of the cancer does not depend upon the radiation dose which caused it.
Stochastic effects are often called linear, zerothreshOld dose response effects. According to the linear, zero-threshold model, every increment of radiation, no matter how small, canic5 with it a corresponding increase in risk of stochastic effect (Cember, 1989).
When the frequency of occurrence or percent response of a stochastic effect is plotted against the increase of dose to obtain the quantitative relationship, a linear dose-response oue (B) of is observed.
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CHAPTER 111 Methodology